In the field of high speed inkjet printing it is desirable to be able to print across the width of the print media in a single pass of the print media past a print station. However, for many applications the desired print width exceeds the width of the available printheads. It is therefore necessary to arrange an array of printheads such that each printhead in the array prints a print swath, and the set of print swaths cover the entire print width. Whenever the printed image is made of a set of print swaths, it is necessary to align or stitch each pair of adjacent print swaths to each other such that the seam between adjacent print swaths is not visible.
For such printing applications, it is desirable to provide some means to accurately align the array of printheads relative to each other to provide consistency in the stitching of the print swaths. Even with improvements in the reliability of the printheads, it is desirable to provide means for removing and replacing individual printheads within the array of printheads. The structure for aligning the printheads into an array should therefore enable individual printheads to be removed from the array and replaced with another printhead with minimal change in the alignment of the printheads and their corresponding print swaths.
Commonly assigned U.S. Pat. No. 8,226,215 (Bechler et al.) provides a structure for aligning a plurality of printheads, with the printheads arranged in two staggered rows of printheads. It uses a printhead baseplate that includes sets of kinematic alignment features, one set for each printhead, to engage with alignment features on the printheads in order to provide repeatable alignment of the printheads.
Even with a fixed alignment of the array of printheads there is some variation in the quality of the stitching. It has been determined that the amplitude of the stitching variation depends in part on the spacing between the nozzle arrays in the two rows of printheads, with a smaller spacing between the rows yielding less variation in the stitching. It has also been found that as the desired print width increases, the cost for manufacturing the alignment baseplate to accommodate the increased print width increases significantly. There remains a need to provide an improved alignment system that can more readily accommodate wider print widths and provide a reduced spacing between the nozzle arrays in the rows of printheads.
In the field of continuous inkjet printing, each printhead includes a drop generator, which includes an array of nozzles, and drop selection hardware, which includes a mechanism to cause, for each of the nozzles in the array, the trajectories of printing drops to diverge from the trajectories of non-printing drops. An ink catcher is used to intercept the trajectory of the non-printing drops from each nozzle. It has been found that a skew of the drop selection hardware relative to the nozzle array can contribute to a skew of the images printed by the printhead relative to the print swaths of other printheads in an array of printheads. There remains a need for an improved system for aligning the drop selection hardware of a printhead relative to the nozzle array of a printhead.
As was pointed out in U.S. Pat. No. 3,596,275 (Sweet), it is desirable to provide a flow of air roughly parallel to the drop trajectory to reduce air drag artifact in the printed image. This air flow is commonly referred to as a collinear airflow, as the air flow being collinear or parallel to the drop trajectories as the air leaves the printhead through the gap between the catcher and the eyelid. Ideally the collinear airflow has a velocity approximately equal to the drop velocity so that the air drag on the print drops is reduced to near zero. The air flow in the region around the drop trajectories should be free from turbulence and should be uniform across the width of the jet array. There remains a need for improved systems for providing collinear airflow that is free from turbulence and that is uniform across the width of the jet array.